Bacillus anthracis spores were recently used as agents of bioterrorism. Among the many negative consequences of these deliberate instances of microbiological sabotage was one positive outcome: not all of the 11 victims with the typically lethal inhalational form of anthrax died. Indeed, the aggressive use of quinolones and other antibiotics coupled with the early recognition of disease resulted in the survival of 6 of the 11 patients. Unfortunately, hundreds of other individuals potentially exposed to the anthrax spores required an extended course of antibiotic therapy. A remaining health concern is that the people who received antibiotic prophylaxis may still present with inhalation anthrax after conclusion of their therapy as dormant viable spores germinate. One way to increase the likelihood that patients with disease will survive and that those exposed will have a higher probability of remaining healthy is to prevent the infectious dormant spores from germinating and subsequently transforming to vegetative cells. Recent evidence that antibodies against the PA (the shared B subunit for the two A subunit toxins of B. anthracis, edema factor and lethal factor) actually bind to the surface of spores and decrease the level of spore germination, taken with the fact that formaldehyde-inactivated spores can serve as a protective vaccine against anthrax in guinea pigs, led us to the following hypothesis: mAbs against PA and/or other spore-surface-expressed antigens can block spore germination or render spores more susceptible to phagocytosis and ultimately killing by macrophages. Based on this theory, our goals are to develop immunoprotective mAbs against B. anthracis spores that confer protection against anthrax in animal models. Ultimately, we intend to humanize those mAbs for use as short-term preventative agents or therapeutic modalities. The Specific Aims are as follows. Specific Aim 1 is to elicit mouse antisera against irradiated B. anthracis dormant spores, irradiated activated spores, activated spore-surface protein extracts, and recombinant PA (rPA). We will test those antisera in enzyme-linked immunosorbent assays (ELISAs), in vitro germination assays, and macrophage assays to evaluate phagocytosis, germination, and sporicidal activity. We will then prepare mAbs from those animals whose sera demonstrate one or more of these anti-spore related activities. Specific Aim 2 is to assess the capacity of these B. anthracis mAbs to prevent anthrax disease first in a mouse parenteral spore challenge model and, if protective, in a rabbit model of inhalational anthrax. Specific Aim 3 is to identify the spore-surface protein(s) recognized by each mAb through N-terminal sequencing. Specific Aim 4 is to initiate, with SUNOL Molecular Corporation, the engineering of humanized versions of those mAbs that confer protection.